Dissolution of Platinum in Presence of Chloride Traces

One of the main issues on the way to a commercial use of fuel cells is the durability of the cell compartments, in particular electrocatalysts. Chloride impurities, originating from airborne salts or synthesis residues, can have severe effects on degradation in general. The quantitative impact on dissolution of Pt, which is the most common electrocatalyst material in polymer electrolyte membrane fuel cells, and the mechanism are still not fully understood. In the current work, potentiodynamic and potentiostatic measurements of platinum in acidic electrolytes containing chlorides in the range of 1 to 1000 μM were carried out utilizing a scanning flow cell (SFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). We show that during potentiodynamic measurements dissolution accelerates with increase in amount of chlorides, as expected. Similarly as in Cl−-free electrolytes, dissolution is a predominantly transient process taking place during oxide formation and reduction. While thus in general the mechanism remains the same as reported before in the absence of chlorides, evidence for additional dissolution processes during oxide formation and reduction are observed. This leads to a variation in the ratio between anodic and cathodic dissolution when chlorides are present. Based on the experimental results a tentative dissolution mechanism is proposed.